Experimental investigation on the choice of the tungsten/rhodium anode/filter combination for an amorphous selenium-based digital mammography system.

The signal difference-to-noise ratio (SDNR) between aluminium sheets and a homogeneous background was measured for various radiation qualities and breast thicknesses to determine the optimal radiation quality when using a Novation DR mammography system. Breast simulating phantoms, with a thickness from 2 cm to 7 cm, and aluminium sheet, with a thickness of 0.2 mm, were used. Three different combinations of anode/filter material and a wide range of tube voltages were employed for each phantom thickness. Each radiation quality was studied using three different dose levels. The tungsten (W) anode and rhodium (Rh) filter combination achieved the specified SDNR at the lowest mean glandular dose for all the phantom thicknesses and X-ray tube voltages. The difference between the doses for different anode/filter combinations increased with the phantom thickness. For a 5-cm phantom, with a peak tube voltage of 27 kV and a SDNR of 5, the mean glandular dose associated with the use of W/Rh was reduced by 49% when compared to the molybdenum/molybdenum (Mo/Mo) anode/filter combination and by 33% when compared to Mo/Rh. Based on these measurements, the use of the W/Rh anode/filter can be recommended. It remains important, however, to select the appropriate dose level.

First preclinical evaluation of mono-[123I]iodohypericin as a necrosis-avid tracer agent.

PURPOSE: We have labelled hypericin, a polyphenolic polycyclic quinone found in St. John's wort (Hypericum perforatum), with( 123)I and evaluated mono-[(123)I]iodohypericin (MIH) as a potential necrosis-avid diagnostic tracer agent. METHODS: MIH was prepared by an electrophilic radioiodination method. The new tracer agent was evaluated in animal models of liver infarction in the rat and heart infarction in the rabbit using single-photon emission computed tomography (SPECT), triphenyltetrazolium chloride (TTC) histochemical staining, serial sectional autoradiography and microscopy, and radioactivity counting techniques. RESULTS: Using in vivo SPECT imaging, hepatic and cardiac infarctions were persistently visualised as well-defined hot spots over 48 h. Preferential uptake of the tracer agent in necrotic tissue was confirmed by perfect match of images from post-mortem TTC staining, autoradiography (ARX) and histology. Radioactivity concentration in infarcted tissues was over 10 times (liver; 3.51% ID/g in necrotic tissue vs 0.38% ID/g in normal tissue at 60 h p.i.) and over 6 times (myocardium; 0.36% ID/g in necrotic tissue vs 0.054% ID/g in normal tissue; ratios up to 18 for selected parts on ARX images) higher than in normal tissues. CONCLUSION: The results suggest that hypericin derivatives may serve as powerful necrosis-avid diagnostic agents for assessment of tissue viability.

Passive somatosensory discrimination tasks in healthy volunteers: differential networks involved in familiar versus unfamiliar shape and length discrimination.

Somatosensory discrimination of unseen objects relies on processing of proprioceptive and tactile information to detect spatial features, such as shape or length, as acquired by exploratory finger movements. This ability can be impaired after stroke, because of somatosensory-motor deficits. Passive somatosensory discrimination tasks are therefore used in therapy to improve motor function. Whereas the neural correlates of active discrimination have been addressed repeatedly, little is known about the neural networks activated during passive discrimination of somatosensory information. In the present study, we applied functional magnetic resonance imaging (fMRI) while the right index finger of ten healthy subjects was passively moved along various shapes and lengths by an fMRI compatible robot. Comparing discriminating versus non-discriminating passive movements, we identified a bilateral parieto-frontal network, including the precuneus, superior parietal gyrus, rostral intraparietal sulcus, and supramarginal gyrus as well as the supplementary motor area (SMA), dorsal premotor (PMd), and ventral premotor (PMv) areas. Additionally, we compared the discrimination of different spatial features, i.e., discrimination of length versus familiar (rectangles or triangles) and unfamiliar geometric shapes (arbitrary quadrilaterals). Length discrimination activated mainly medially located superior parietal and PMd circuits whereas discrimination of familiar geometric shapes activated more laterally located inferior parietal and PMv regions. These differential parieto-frontal circuits provide new insights into the neural basis of extracting spatial features from somatosensory input and suggest that different passive discrimination tasks could be used for lesion-specific training following stroke.

Evaluation of radiofrequency ablation as an alternative for the treatment of brain tumor in rabbits.

Radiofrequency ablation (RFA) has emerged recently as a promising therapy for extracranial malignancies. This experiment was conducted to explore the potential of RFA for the treatment of brain tumor in a rabbit model with imaging-histological assessment. Eighteen rabbits with intracranially implanted VX2 tumors of 0.9+/-0.2 cm in diameter were divided into two groups. Group A (n = 12) was treated with a cooled-tip RFA technique at 30 watts for 30-60 s. Group B (n = 6) received sham operation. The therapeutic efficacy was evaluated by comparing survival rate, magnetic resonance imaging (MRI) and histological findings. All animals in Group B died within one month after tumor implantation (19+/-2.6 days). Tumor eradication was achieved in 6/12 rabbits (50.0%) in Group A, of which three rabbits survived longer than three months, another three rabbits were found free of viable tumor when sacrificed. Five rabbits suffered from local tumor relapse. One rabbit developed intracranial metastasis to the brain stem despite a complete ablation of the original tumor. Three-month survival rate of RFA treated rabbits was significantly higher (p < 0.05) than that of control rabbits. The typical MRI appearances of the acute RFA lesion consisted of three characteristic concentric zones, which corresponded to central coagulative tissues (Zone A), peripheral hemorrhagic rim (Zone B) and interstitial edema (Zone C) on histology. This study suggests that RFA may become a promising alternative therapy for the treatment of brain tumor. The recognized characters of thermal lesion on MRI and histology may prove valuable in delimitating the ablation range and understanding the biological response of the RFA.